Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$224.55	12.134%	$251.7969	$251.80	$251.80	$251.80
Purchase #2	$96.71	6.712%	$103.2012	$103.20	$103.20	$103.20
Purchase #3	$85.96	3.868%	$89.2849	$89.28	$89.30	$89.30
Purchase #4	$157.96	8.774%	$171.8194	$171.82	$171.80	$171.80
Purchase #5	$109.27	12.630%	$123.0708	$123.07	$123.05	$123.10
Purchase #6	$32.29	13.748%	$36.7292	$36.73	$36.75	$36.70
Purchase #7	$189.90	8.238%	$205.544	$205.54	$205.55	$205.50
7 purchase totals =	$896.64		$981.4464	$981.44	$981.45	$981.40